There are a number of medicament delivery devices on the market by which a user may set a dose of medicament to be delivered. Also many devices are capable of delivering a number of doses from a medicament container until it becomes empty. In this respect, each dose could have the same size, i.e. a fixed dose size or each dose could be individually set before delivery.
The majority of the devices developed for this purpose are provided with dose setting knobs, often placed in the distal end of the devices and intended to be turned or rotated in order to set a dose to be delivered. However, a turning motion is not always the optimum for some users, such as for example with reduced dexterity. It might then be difficult to actually set the desired and prescribed dose if the precision in the hands are gravely reduced due to e.g. rheumatism. Also, the turning motion is widely used because of the design of many delivery devices having generally tubular shapes and rotating components.
Another drawback with some known delivery devices is that it may require considerable force from the user for performing certain operations such as cocking or arming a device and/or subsequent injection.
One solution to the latter drawback is disclosed in US 2005/0165363. Here a manually operable piston, which is used for performing an injection, is operably connected to a drive member, which acts on a stopper in a medicament container for expelling medicament through a medicament delivery member, such as an injection needle. In order to facilitate the operation of the device also for users having reduced strength a gear set is arranged between the piston and the drive member, which gear set then reduces the force required for the operation. However there is no possibility of setting a dose.
There are several other documents disclosing different types of force reducing transmissions comprising toothed racks and cog-wheels, such as U.S. Pat. No. 5,782,633, WO 03/080160, WO96/26754 and WO 2008/058666. however, none of these documents disclose a transmission or function wherein the handling of a dose setting member or actuation member for setting a prescribed dose a certain distance, linear or rotational provides a linear or rotational distance that a dose providing member is moved, such as a driver acting on a plunger rod. This has proved a drawback, especially when rather small doses of medicament are to be set, whereby the accuracy of the dose setting distance cannot be guaranteed. It would be an advantage if the accuracy could be enhanced with this type of movement transmissions utilizing toothed racks and cog-wheels.